Abstract
Eelgrass meadows play key roles in coastal ecosystems, and the extent of the standing biomass is focal to address ecosystem functioning. Eelgrass cover is commonly assessed in marine monitoring programs while biomass sampling is destructive and expensive. Therefore, we have proposed a functional relationship that translates eelgrass cover into aboveground biomass using site-specific information on Secchi depth or light attenuation. The relationship was estimated by non-linear regression on 791 combined observations of eelgrass cover and biomass from eight different coastal sites in Denmark. Eelgrass biomass initially increased with cover and flattened out as cover exceeded 40–50 % due to increased self-shading. Decreasing light energy with depth reduced the eelgrass biomass potential (assessed at 100 % cover), and this reduction was stronger for coastal sites with lower water transparency. Moreover, the biomass potential varied seasonally from around 110–140 g DW m−2 in spring months to a peak of 241 g DW m−2 in August, consistent with other seasonal studies. The model explained 56 % of the variation in log-transformed biomasses, but significant variation between coastal sites still remained, deviating between −23 and 39 % from the mean relationship. These site-specific deviations could be due to differences in losses related to grazing, drifting algae and epiphytes, better light capture by dense canopies, as well as differences in how well light conditions within eelgrass meadows are represented by actual measurements of Secchi depth and light attenuation. The relationship can be employed to estimate eelgrass biomass of entire coastal ecosystems from observations of eelgrass cover and depth.
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Acknowledgments
We are grateful to Nikolaj Holmboe, Steen Schwaerter, Jens Sund Laursen, Mikael Hjort Jensen, and Martha Laursen from the local departments of the Danish Nature Agency for their help on providing data and background information on eelgrass in the various coastal areas. We thank three anonymous reviewers and the associate editor for their constructive comments that improved the manuscript. The study received support from the Danish Nature Agency, the DEVOTES project funded under the EC 7th framework program (grant agreement no. 308392) and the COCOA project under the BONUS research program funded by the EC and the Danish Research Council.
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Communicated by Alberto Vieira Borges
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Carstensen, J., Krause-Jensen, D. & Balsby, T.J.S. Biomass-Cover Relationship for Eelgrass Meadows. Estuaries and Coasts 39, 440–450 (2016). https://doi.org/10.1007/s12237-015-9995-6
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DOI: https://doi.org/10.1007/s12237-015-9995-6